Add basic examples and description of usage to the README.

README.md

@@ -6,22 +6,101 @@ A Python module for decorators, wrappers and monkey patching.
 Overview
 --------
 
-The aim of the **wrapt** module is to provide a transparent object proxy
-for Python, which can be used as the basis for the construction of function
-wrappers and decorator functions.
+The aim of the **wrapt** module is to provide a transparent object proxy for Python, which can be used as the basis for the construction of function wrappers and decorator functions.
 
-The **wrapt** module focuses very much on correctness. It therefore goes
-way beyond existing mechanisms such as ``functools.wraps()`` to ensure that
-decorators preserve introspectability, signatures, type checking abilities
-etc. The decorators that can be constructed using this module will work in
-far more scenarios than typical decorators and provide more predictable and
-consistent behaviour.
+The **wrapt** module focuses very much on correctness. It therefore goes way beyond existing mechanisms such as ``functools.wraps()`` to ensure that decorators preserve introspectability, signatures, type checking abilities etc. The decorators that can be constructed using this module will work in far more scenarios than typical decorators and provide more predictable and consistent behaviour.
 
-To ensure that the overhead is as minimal as possible, a C extension module
-is used for performance critical components. An automatic fallback to a
-pure Python implementation is also provided where a target system does not
-have a compiler to allow the C extension to be compiled.
+To ensure that the overhead is as minimal as possible, a C extension module is used for performance critical components. An automatic fallback to a pure Python implementation is also provided where a target system does not have a compiler to allow the C extension to be compiled.
 
+Examples
+--------
+
+To implement your decorator you need to first define a wrapper function. This will be called each time a decorated function is called. The wrapper function needs to take four arguments:
+
+* ``wrapped`` - The wrapped function which in turns needs to be called by your wrapper function.
+* ``instance`` - The object to which the wrapped function was bound when it was called.
+* ``args`` - The list of positional arguments supplied when the decorated function was called.
+* ``kwargs`` - The dictionary of keyword arguments supplied when the decorated function was called.
+
+The wrapper function would do whatever it needs to, but would usually in turn call the wrapped function that is passed in via the ``wrapped`` argument.
+
+The decorator ``@wrapt.decorator`` then needs to be applied to the wrapper function to convert it into a decorator which can in turn be applied to other functions.
+
+    import wrapt
+    
+    @wrapt.decorator
+    def pass_through(wrapped, instance, args, kwargs):
+        return wrapped(*args, **kwargs)
+
+    @pass_through
+    def function():
+        pass
+
+If you wish to implement a decorator which accepts arguments, then list the arguments after the existing four arguments of the wrapper function.
+
+    import wrapt
+    
+    @wrapt.decorator
+    def with_arguments(wrapped, instance, args, kwargs, myarg1, myarg2):
+        with lock:
+            return wrapped(*args, **kwargs)
+
+    @with_arguments(1, 2)
+    def function():
+        pass
+
+It is possible to use positional arguments, with or without default values, a variable arguments list or a keyword argument dictionary.
+
+Any arguments given to your decorator when it is used to decorate a function, will be passed to the wrapper via the arguments added to the wrapper function, when the wrapper is invoked upon the call of the decorated function.
+
+Note that even if all your decorator arguments have default values, or you only have a variable arguments list or keyword argument dictionary, you must still provide the parantheses to the decorator when used. Once you opt to have the decorator be able to accept arguments the use of the parentheses is not optional.
+
+if using Python 3, you can use the keyword arguments only syntax to force use of keyword arguments when the decorator is used.
+
+    import wrapt
+    
+    @wrapt.decorator
+    def with_arguments(wrapped, instance, args, kwargs, *, myarg1, myarg2):
+        with lock:
+            return wrapped(*args, **kwargs)
+
+    @with_arguments(myarg1=1, myarg2=2)
+    def function():
+        pass
+ 
+Any decorator you create can be applied to normal functions, instance methods, class methods, static methods or classes.
+
+When applied to a normal function or static method, the wrapper function when called will be passed ``None`` as the ``instance`` argument.
+
+When applied to an instance method, the wrapper function when called will be passed the instance of the class the method is being called on as the ``instance`` argument. This will be the case even when the instance method was called explicitly via the Class and the instance passed as the first argument. That is, the instance will never be passed as part of ``args``.
+
+When applied to a class method, the wrapper function when called will be passed the class type as the ``instance`` argument.
+
+When applied to a class, the wrapper function when called will be passed ``None`` as the ``instance`` argument. The ``wrapped`` argument in this case will be the class.
+
+The above rules can be summarised with the following example.
+
+    @wrapt.decorator
+    def universal(wrapped, instance, args, kwargs):
+        if instance is None:
+            if isinstance(wrapped, type):
+                # Decorator was applied to a class.
+                return wrapped(*args, **kwargs)
+            else:
+                # Decorator was applied to a function or staticmethod.
+                return wrapped(*args, **kwargs)
+        else:
+            if isinstance(instance, type):
+                # Decorator was applied to a classmethod.
+                return wrapped(*args, **kwargs)
+            else:
+                # Decorator was applied to an instancemethod.
+                return wrapped(*args, **kwargs)
+
+Using these checks it is therefore possible to create a universal decorator that can be applied in all situations. It is no longer necessary to create different variants of decorators for normal functions and instance methods. 
+
+In all cases, the wrapped function passed to the wrapper function is called in the same way, with ``args`` and ``kwargs`` being passed. The ``instance`` argument doesn't need to be used in calling the wrapped function.
+                
 Testing
 -------